Gravel pack systems allow many downhole procedures to take place in a single trip. A gravel pack assembly typically contains sections of screen that extend from an isolation packer. An inner string that includes a crossover tool is movable with respect to the set packer for selective sealing relation with a polished bore in the packer. In this manner fluids can be circulated when the assembly is run in and gravel can be deposited outside the screens while return fluids can come up through the screens and up a wash pipe. These return fluids can then pass through a valve in an uphole direction and go through the crossover and back to the surface through the annulus above the set packer. Alternatively, the crossover can allow the gravel to be deposited with fluid squeezed into the formation in a procedure called a frac pack. The crossover is simply positioned with respect to the isolation packer in a manner where no return port through the wash pipe and back to the surface is open.
Regardless of whether the gravel is deposited with fluid returns to the surface or whether the fluid is forced into the formation when the gravel is deposited outside the screens, the excess gravel in the string leading down to the crossover has to be removed, typically by a process called reversing out. In this step the crossover is repositioned so that fluid pumped from the surface in the annular space above the packer is allowed into the tubing above the packer so that the excess gravel can be brought to the surface. However, performing this procedure can build pressure near the crossover and a risk of fluid loss to the formation with this built up pressure is a possibility. Fluid loss to the formation can diminish its productivity and excessive fluid loss to the formation may inhibit or prevent reverse circulating of the excess gravel from the workstring. For these reasons a fluid loss control valve in the wash pipe extending into a packer seal bore from the crossover has been used. These fluid loss control valves are illustrated in patents relating to gravel packing operations such as U.S. Pat. Nos. 7,290,610; 7,128,151; 7,032,666 and 6,983,795.
One type of valve that has been used is a flapper type. It has been sold by Baker Oil Tools under the name Flapper Anti-Swabbing Tool. This valve is part of the wash pipe and is run in held open. It is positioned below the seal bore on the packer. When it is time to close it the string is pulled up from the surface relative to the set packer. Collets associated with the valve and mounted to its exterior land on a shoulder just below the seal bore so that resistance to further pulling can be experienced at the surface to know that the valve is in position for release. This step was done before the gravel pack was delivered to the annulus outside the screens. A further pull trapped the collet heads against a shoulder adjacent the seal bore and allowed the valve body to shift relative to the collets. This relative movement resulted in breaking a shear pin and allowing a recess on the body to move adjacent the collet heads so that they could collapse radially toward the body so that the wash pipe could come up into the seal bore. The relative movement also freed the flapper to be biased by a pivot spring to go to the closed position.
The problem with this tool is that to see a surface signal a significant tensile force must be pulled and by pulling against a shear pin to generate a force in excess of 21,000 pounds, the string would stretch before the shear pin sheared. When the shear pin sheared, the flapper would go immediately closed but the stretched string would recoil to its original length. The result of these motions was to induce flow out of the formation due to a pressure reduction caused by a now closed string recoiling up through the seal bore. In certain unconsolidated formations this movement induced sand to come into the wellbore around the screens in the very place around the screens where the gravel needed to go. Once that happened it became difficult or impossible to have an effective gravel pack.
What was needed and provided by the present invention is a fluid loss valve that could give a surface signal that it has been released to close but at the same time prevented the phenomenon of drawing sand into the annulus before the gravel pack was accomplished. The present invention breaks up the signal portion at the surface and the actual movement downhole to avoid or minimize the drawing in solids issue. In the preferred embodiment the upward pull against a radial surface still gives the surface signal without and actual release. A subsequent downward movement of the tubing string allows the collets to retract inwardly to eventually clear the seal bore but takes away string tension at the time of release of the collets. The valve can selectively close either when tension is pulled without release or subsequently when tension is released. After gravel packing and reversing out the excess gravel, the wash pipe with the fluid loss valve can be pulled from the packer seal bore without interference. These and other aspects of the present invention will become more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings that appear below while recognizing that the claims define the full literal and equivalent scope of the invention.